Thermoplastic polyurethane (TPU) compositions are highly useful materials that can provide an attractive combination of physical properties. TPUs may be generally described as segmented copolymers, having one or more low glass transition temperature (Tg) soft segments and one or more high Tg hard segments.
There is a continuing need to provide improved TPU compositions that provide improved physical properties, that are easier to process, that are easier to scale to commercial quantities, that can be made via a continuous process, that are more versatile in how they can be used with other materials, or some combination thereof.
There is an ongoing need for TPU compositions that can be more easily processed, and which have improved processing windows, and more specifically, can be scaled to continuous commercial quantity processes. Many TPU compositions have very narrow processing windows, a very tight set of conditions under which they process well. Small changes in processing conditions, which cannot always be easily controlled, can lead to significant variations in product quality. Thus, there are many TPU compositions that could be made in the lab, and which could have interesting combinations of properties, but which effectively cannot be commercialized because they cannot be produced in commercially effective processes.
Thus, there is a need for TPU compositions that can be more easily processed, and which have improved processing windows, which are not as sensitive to changes in processing conditions, including developing TPU compositions with desired combinations of properties that can be produced in commercially effective processes, for example, continuous reactive extruders.
Also, there is an ongoing need for softer TPU compositions that can be easily processed. It is understood that as the amount of hard segment in the TPU is increased, the resulting material gets harder and harder, and likewise, reducing the amount of hard segment in the TPU can result in softer and softer TPU. However, there is a lower limit of hardness that can be reached by changing the hard segment content or type or soft segment content and type. Below this lower limit, the TPU starts losing its strength and becomes too sticky. It becomes more difficult to handle and process, due to the increased stickiness, etc., and eventually becomes impossible to process and/or manufacture. Thus, this lower limit prevents the production and use of “ultra-soft” TPU compositions.
Traditionally, the lowest hardness that can be achieved in a processable TPU without using plasticizer is about Shore 65-70A. However, production of even these TPU compositions is very challenging due to lower solidification or crystallization rates and ever present sticking issues (the TPU composition literally sticks to all equipment surfaces it contacts and to itself). Using a plasticizer in the TPU composition can bring the hardness down to lower values but often times plasticizers are not desired due to their toxicity (phthalate type plasticizers in particular are relatively toxic and not acceptable in many applications) and/or incompatibility (many plasticizers cause blooming in the resulting TPU composition).
Thus, there is always a need for more processable (i.e., extrudable, moldable, etc.), ultra-soft (i.e., Shore hardness below 65A), TPU compositions and methods of making the same. There is particularly a need for plasticizer-free TPU compositions that are ultra-soft and processable. There is also a need for crosslinked TPU networks made from such TPU's and processes of making the same. The present invention addresses these needs.
There is an ongoing need for TPU compositions that can be easily cross-linked. One method of providing cross-linkable TPU compositions is to graft a cross-linkable group or moiety onto the TPU itself and then cross-linking the groups to give a cross-linked TPU network. However, many cross-linkable groups or moieties, like vinyl alkoxysilane moieties, are difficult or even impossible to graft on to TPU compositions.
Thus, there is a need for a TPU compositions that can be easily grafted with a cross-linkable group or moiety, like a vinyl alkoxysilane moiety, thus allowing for easily cross-linkable TPU compositions.
There is also a need to provide a TPU that is more compatible with other polymers, particularly polyolefins. Blending TPU compositions, which are generally considered to be expensive materials, with less expensive materials, for example, polyolefins is an attractive goal for many manufactures that make products from TPU compositions. The blend would be less expensive than using all TPU to make their products. However, TPU compositions generally have poor compatibility with other polymers like polyolefins, resulting in blends that process poorly, have poor physical properties, or other drawbacks.
Thus, there is a need for TPU compositions that have improved compatibility with other polymers like polyolefins, thus allowing for the preparation and use of blends containing TPU compositions and polymers like polyolefins, while still maintaining the physical properties and quality required by manufactures that make products from TPU compositions.
There is a need for TPU compositions that can be easily cross-linked. As noted above, one method of providing cross-linkable TPU compositions is to graft a cross-linkable group or moiety onto the TPU itself and then cross-linking the groups to give a cross-linked TPU network. However, many cross-linkable groups or moieties, like vinyl alkoxysilane moieties, are difficult or even impossible to graft on to TPU compositions. In addition, this grafting step, even if it can be done easily, adds cost and complexity. A more ideal result would be a TPU that is readily cross-linkable without the need for a grafting step at all.
Thus, there is a need for TPU compositions that are easily cross-linkable with the need to graft a group or moiety onto the TPU first.
Various embodiments of the invention described herein address one or more of the needs described above.